All issues
Volume 44, Issue 1
Displaying 1-22 of 22 articles from this issue
- |<
- <
- 1
- >
- >|
-
Hitoshi Taguchi, Taku Takeishi, Kenichiro Suwa1997 Volume 44 Issue 1 Pages 3-10
Published: January 15, 1997
Released on J-STAGE: December 04, 2009
JOURNAL OPEN ACCESSThis paper reviews recent research at TDK on high performance ferrite magnets. First, new processes forachieving submicron-sized particles, high orientation and high density were studied in detail. As a result, high performance Sr-ferrite magnets with Br=0.44T (4.4kG) and HcJ=320kA/m (4.0kOe) were developed. Furthermore, by means of SiO2-SrO or SiO2-BaO addition, high performance Ba-ferrite magnets with Br=0.43T (4.3kG), HcJ=290kA/m (3.6kOe) were obtained. At the same time, we discovered that it is possible to make equal the shrinkage ratio in the a- and c-axes. Second, (LiFe)ZnW-ferrite and Zn-substituted M-ferrite were investigated. Consequently, LaZn substituted SrM ferrite magnets were developed with extremely good properties, viz. Br=0.46T(4.6kG) and (BH)max=41kJ/m3(5.2MGOe).View full abstractDownload PDF (3001K) -
Hiroshi Yamamoto, Masaki Kaneko1997 Volume 44 Issue 1 Pages 11-16
Published: January 15, 1997
Released on J-STAGE: December 04, 2009
JOURNAL OPEN ACCESSBa-M ferrite fine particles were prepared by mechanical compounding method using the planetary ball-mill and subsequent heat treatment. The conditions determined as optimum for the preparation of Ba-M ferrite fine particles having a somewhat similar diameter to the single domain are as follows : chemical composition-BaO⋅5Fe2O3 ; planetary ball-mill condition : 300rpm×lh ; heating condition : 1100°C×1h in air ; magnetic and physical properties are σs=82.5×10-6wb⋅m/kg, HcJ=326.3kA/m, Tc=450.6°C, lattice constant a=5.874×10-10m, c=23.22×10-10m and average particle size 0.41μm.View full abstractDownload PDF (2698K) -
Sachio Toyota1997 Volume 44 Issue 1 Pages 17-21
Published: January 15, 1997
Released on J-STAGE: December 04, 2009
JOURNAL OPEN ACCESSAs W-type hexagonal ferrite permanent magnets with the formula SrO⋅2FeO⋅8Fe2O3 contain both ferrous and ferric oxides, a complicated atmosphere control during the sintering process is necessary in manufacturing, which is impractical for industrial production. Thus, a simple manufacturing method which is characterized by employing a combination of the addition of carbon and the adoption of nitrogen atmosphere in sintering was investigated, so that high performance permanent magnets were successfully prepared. It was found that the additional amount of carbon and the heating temperature for drying green body are closely associated with oxidation and reduction in the sintering process. The unfitted conditions for synthesis are apt to produce extra phase, such as hematite and magnetite which influence magnetic properties. Especially, small amounts of magnetite which are produced by a reduction phenomenon during the sintering process decrease coercivity remarkably. A pure W-phase was formed by addition of 0.2wt% carbon and drying green body at 200°C for 3h. The highest magnetic properties obtained by the present work are remanence of 0.48T (4.8kG), coercivity of 200kA/m (2.5kOe) and the maximum energy product of 42kJ/m3 (5.3MGOe).View full abstractDownload PDF (2168K) -
Hirofumi Kakuta, Ryo Murakami, Hitoshi Takamura, Terumi Tanaka, Motofu ...1997 Volume 44 Issue 1 Pages 22-26
Published: January 15, 1997
Released on J-STAGE: December 04, 2009
JOURNAL OPEN ACCESSThe crystal structure and magnetic properties of Zn-stabilized La M-type ferrite with magnetoplumbite structure were studied. The single phase of M-type ferrite was obtained by using conventional ceramic techniques with nominal composition of LaZn0.5Fe11.3 O19. It was confirmed that the Zn-stabilized La M-type ferrite had a hexagonal symmetry (P63/mmc) with lattice constants of a=0.5890, c=2.2926nm. The c-axis length was smaller than that of Sr or Ba M-type ferrite. The magnetization of this ferrite is 81.4μWb⋅m⋅kg-1 at room temperature at the applied field of 1200kA⋅m-1, and the Curie temperature is 649K.View full abstractDownload PDF (1597K) -
[in Japanese]1997 Volume 44 Issue 1 Pages 28
Published: January 15, 1997
Released on J-STAGE: May 22, 2009
JOURNAL OPEN ACCESSDownload PDF (81K) -
Shigeru Katsuyama, Yoichi Shichijo, Teruhisa Ichise, Kazuhiko Majima, ...1997 Volume 44 Issue 1 Pages 29-33
Published: January 15, 1997
Released on J-STAGE: December 04, 2009
JOURNAL OPEN ACCESSThe effect of mechanical grinding (MG) on the thermoelectric properties of the skutterudite material CoSb3 was examined. The sign of the thermoelectric power (a) of CoSb3 which was not exposed to MG treatment (no-MG-sample) was positive, while that of CoSb3 which was exposed to MG treatment (MG-sample) was negative. With an increase of temperature, the electrical resistivity (ρ) of no-MG-sample increases, but that of MG-sample decreases. The thermal conductivity (k) of the material was decreased by MG treatment, which are ascribed to the decrease of the grain size by the MG treatment. The figure of merit (Z=α2/(ρ⋅k)) of no-MG-sample is larger than that of MG-sample in the temperature range from room temperature to 500°C.View full abstractDownload PDF (283K) -
Hiroshi Nagai, Takashi Tahata, Tomohide Nishikawa, Shigeru Katsuyama, ...1997 Volume 44 Issue 1 Pages 34-38
Published: January 15, 1997
Released on J-STAGE: May 22, 2009
JOURNAL OPEN ACCESSThe effects of Ti, Zr and Nb addition on the thermoelectric properties of β-FeSi2 were investigated. Mixture of Fe and Si powders with composition of Fe1-xSi2 was arc-melted in an argon atmosphere to form a button composed of α-Fe2Si5 and ε-FeSi phases. The button was ground under -60mesh and Ti, Zr or Nb powders were mixed for Fe1-xMxSi2(M=Ti, Zr, Nb, 0≤X≤1.8). Then, the mixed powders were groun(MA) in a vibrational mill (SPEX-8000) for 36 ks. β-FeSi2 phase was not formed during MA, but was obtained by hot pressing of MA powders at 1173 K for 1.8 ks under 25MPa. It was found that Zr addition drastically changed the thermoelectric properties of FeSi2, especially the temperature dependence of resistivity and thermoelectric power, while addition of Ti and Nb showed rather deleterious effect on the thermoelectric properties of β-FeSi2. Zr addition extremely decreased the resistivity(ρ), although thermoelectric power(Q) decreased with increasing Zr addition. As the result, Zr addition increased the power factor(Q2/ρ) of β-FeSi2, especially at high temperatures. On the other hand, since the increase in thermal conductivity(K) by Zr addition was not apparent, figure of merit(Q2/ρK) of, B -FeSi2 increased with increasing Zr addition and showed the same tendency as the power factor. EPMA and XRD revealed that Fel.xMxSi2 (M=Ti, Zr, Nb) was composed of β-FeSi2 matrix with dispersion of TiSi2, ZrSi2 or NbSi2 particles.View full abstractDownload PDF (267K) -
Hirotsugu Takizawa, Kenta Yamamoto, Tadashi Endo, Masahiko Shimada1997 Volume 44 Issue 1 Pages 39-43
Published: January 15, 1997
Released on J-STAGE: May 22, 2009
JOURNAL OPEN ACCESSβ-FeSi2 was sintered under high-pressure/ temperature conditions of 3 GPa and 700-1400°C for 30 min using a belt-type high-pressure equipment. The material showed anisotropy due to heterogeneous distribution of pressure, however, the X-ray diffraction analysis did not reveal crystallographic orientation. The microstructure showed grain orientation along the direction perpendicular to the pressing direction. Such orientation was remarkable in the sample solidified from the melt. It was suggested that the development of microstructure was important factor in optimizing the thermoelectric properties. The formation and the phase stability of β-FeSi2 under high-pressure condition were also discussed.View full abstractDownload PDF (2920K) -
Hidenori Hiramatsu, Hiromichi Ohta, Won-Seon Seo, Kunihito Koumoto1997 Volume 44 Issue 1 Pages 44-49
Published: January 15, 1997
Released on J-STAGE: May 22, 2009
JOURNAL OPEN ACCESSWe have reported that the thermoelectric figures of merit (Z) of the sintered bodies of layered structured (ZnO)mIn2O3, (m=5, 7, and 9) are comparatively large among the semiconducting oxides. In this work, (ZnO)5In2O3 thin films were prepared by r.f. (radio frequency) sputtering method to clarify their anisotropic nature. Under optimum sputtering conditions, (ZnO)5In2O3 thin films developed either (0021) or (110) crystallographic preferred orientation and had dense columnar structures. For c-axis and ab-plane oriented (ZnO)5In2O3 thin films, Seebeck coefficient (α) and electrical conductivity (σ) along the sheet direction were measured at 573-973K. Electrical conductivity of a c-axis oriented thin film was about an order of magnitude higher than that of an ab-plane oriented thin film, while their Seebeck coefficients were substantially the same. This observation suggests that the carrier mobility of (ZnO)5In2O3 along the c-plane is larger than along the ab-plane.View full abstractDownload PDF (2037K) -
Masahiro Yasukawa, Norimitsu Murayama1997 Volume 44 Issue 1 Pages 50-54
Published: January 15, 1997
Released on J-STAGE: December 04, 2009
JOURNAL OPEN ACCESSThermoelectric power factor and figure of merit of Nd2-xCexCuO4 (x=0-0.1) sintered bodies were estimated from the Seebeck coefficient, electrical resistivity, and thermal conductivity measured in temperature range of 300-673 K. Temperature dependence of Seebeck coefficient and electrical resistivity showed n-type semiconducting behavior. Thermal conductivities, which decreased with increasing temperature for each Cc concentration, were in range of 3.7-7.5 Wm-1K-1. The power factor and the figure of merit for x=0.01 and 0.05 increased with decreasing temperature. Their maxima were 9.2⋅10-5 Wm-1K-2 and 1.7⋅10-5K-1, respectively, at 320 K for x=0.05. The figure of merit would be improved to some extent by reduction of lattice thermal conductivity.View full abstractDownload PDF (255K) -
Lidong Chen, Takashi Goto, Jianhui Li, Toshio Hirai1997 Volume 44 Issue 1 Pages 55-59
Published: January 15, 1997
Released on J-STAGE: May 22, 2009
JOURNAL OPEN ACCESSSilicon borides were prepared by arc melting in argon atmosphere using silicon and boron powders in a boron content range from 80 to 94mol%. As-melted specimens consisted of SiBn, and free Si. The contents of free Si decreased from 30 to 3vol% as the boron content in raw material increased from 80 to 94mol%. The as-melted specimens were heat-treated in argon atmosphere at temperatures of 1400 to 1700K. During heat treatment, free Si reacted with SiBn near the SiBn-Si boundary to form SiB4, and as the result SiBn, -SiB4 composites were obtained. The SiBn-SiB4 composites showed larger electrical conductivity and smaller thermal conductivity than the as-melted specimens, which contributes to improvement of thermoelectrical property.View full abstractDownload PDF (1260K) -
Takashi Goto, Jianhui Li, Toshio Hirai1997 Volume 44 Issue 1 Pages 60-64
Published: January 15, 1997
Released on J-STAGE: May 22, 2009
JOURNAL OPEN ACCESSB4C-TiB2 quasi-binary composites were prepared by arc melting in argon atmosphere using B4C and TiB2 powders. Uniform lamella texture indicating eutectic reaction was observed at 25mol%TiB2 in the quasi-binary system. The electrical conductivity of the B4C-TiB2 composites significantly increased with increasing TiB2 content. The thermal conductivity (κ) of the composites containing 2mol%TiB2 was slightly smaller than that of B4C, but the κ values increased with increasing TiB2 content at more than 6mol%. The Seebeck coefficient of B4C-TiB2 composites showed maxima at 6mol%TiB2. The thermoelectric figure-of-merit (Z) values exponentially increased with increasing temperature, showing maxima at 6mol%TiB2. The greatest ZT values obtained in the present study was 0.55 at T=1100K for the composite containing 6mol%TiB2.View full abstractDownload PDF (1402K) -
Takashi Goto, Jianhui Li, Toshio Hirai, Yukio Maeda, Ryozo Kato, Akika ...1997 Volume 44 Issue 1 Pages 65-69
Published: January 15, 1997
Released on J-STAGE: December 04, 2009
JOURNAL OPEN ACCESSAn ac method for the measurement of the Seebeck coefficient was developed. Specimens were heated periodically at frequencies in the range 0.2 - 10 Hz using a semiconductor laser. The small temperature increase and the resultant thermoelectric power were measured with a Pt-Pt13%oRh, thermocouple (25 μm in diameter) through a lock-in amplifier. The Seebeck coefficient of a Pt90Rh10 foil measured by the ac method was in agreement with that obtained from the standard table. The optimum frequency and specimen thickness for the ac method were 0.2 Hz and 0.1 - 0.2 mm, respectively. The Seebeck coefficients of silicon single crystal and several thermoelectric semiconductors (Si80Ge20, PbTe, FeSi2, SiB14) measured by the ac method agreed with those measured by a conventional dc method in the temperature range between room temperature and 1200 K. The time needed for each measurement was less than a few tens of minutes, significantly shorter than that for a conventional dc method.View full abstractDownload PDF (267K) -
Sunao Sugihara, Hiromichi Kiyozuka, Kiyoshi Okazaki1997 Volume 44 Issue 1 Pages 73-78
Published: January 15, 1997
Released on J-STAGE: May 22, 2009
JOURNAL OPEN ACCESSThe purpose of present study is to sinter BaTiO3 ceramics at lower temperature than the conventional one. The lower temperature sintering was performed by adding lead boro-silicate glass to BaTiO3, and dielectric properties were evaluated for every content of the glass (0.3. 0.6 and 1.2 mol%). The effects of the glass are more significant in the lower sintering temperature such as 1273K. In particular, 1.2 mol% addition of the glass enhanced a relative permittivity which was 1600 at 1 KHz and a dielectric loss up to 1 MHz were not inferior to those of specimens sintered at 1473 K. The dielectric loss was about 3 % at the frequencies more than 10 kHz. The effects of a glass are discussed with the model for the two phases such as BaTiO3, and grains or pore by the equivalent curcuit.View full abstractDownload PDF (2764K) -
Yong-Ho Park, Tae-Young Um, Hitoshi Hashimoto, Toshihiko Abe, Cha-Hurn ...1997 Volume 44 Issue 1 Pages 79-85
Published: January 15, 1997
Released on J-STAGE: May 22, 2009
JOURNAL OPEN ACCESSMoSi2 is one of the-most promising candidate for high-temperature structural materials because of its high melting points and excellent oxidation resistance. However, the low room temperature fracture toughness and ductility, etc. of MoSi2 still remains as major obstacles to potential high temperature structural applications. The fracture toughness of brittle matrix can be improved by the incorporation of a ductile second phase such as metallic Nb. The purpose of this study is to improve the room temperature fracture toughness and ductility of sintered MoSi2 and MoSi2/Nb composites respectively by densification, refining of microstructure and minimizing of interfacial reactions between matrix and Nb. These compound and composite are prepared by mechanical alloying(MA)-spark plasma sintering(SPS) process. The microstructures and material properties of these samples were investigated by optical microscopy, SEM, XRD, EPMA, microhardness measurement and 4-point bending test. The Vickers hardness, bending strength and fracture toughness increased with the incorporation of metallic Nb.View full abstractDownload PDF (3325K) -
Akira Watazu, Hiroshi Masunoto, Yoichiro Masuda, Akira Baba, Takashi G ...1997 Volume 44 Issue 1 Pages 86-89
Published: January 15, 1997
Released on J-STAGE: May 22, 2009
JOURNAL OPEN ACCESSBa-Na-Nb-O thin films were formed on sapphire (1120) substrates by electron cyclotron resonance plasma sputtering by using ring shaped targets. A Ba2NaNb5O15 (BNN) thin film of single phase was obtained at the substrate temperature of 873 K by using the target composition of Ba : Na : Nb = 1.0 : 1.0 : 5.0. The (001) oriented BNN film was successfully obtained at 923 K. The contents of Ba and Nb in the films were independent of substrate temperature in the range between 298 K and 923 K. However, Na content decreased with increasing substrate temperature. Deposition rates of the BNN thin films were estimated to be about 1.0X10-1 nm/s. The absorption edge of the BNN films deposited at 923 K became clear in the vicinity of 300 nm. The transmittance in the wavelength between 700 and 2000 nm have exceedingly by more than 80%. The refractive index of the film was estimated about 2.07 at 627 nm.View full abstractDownload PDF (1300K) -
Akihiko Saguchi, Wataru Takahashi, Yuji Kaneko, Naoyuki Ishigaki1997 Volume 44 Issue 1 Pages 90-95
Published: January 15, 1997
Released on J-STAGE: May 22, 2009
JOURNAL OPEN ACCESSThe powder metallurgical process has been used to produce Nd-Fe-B sintered permament magnet. Therefore, fine magnetic powders (3-4 μm) are required to be pulverized from Nd-Fe-B casting alloy. At present, a combination of hydrogen decrepitation(HD) and mechanical milling has been applied to make fine powders efficently. In our previous work, the fundamental hydrogen absorbing mechanism into Nd-Fe-B alloy was successfully studied by using P-C-Tequipment. In this paper, the influences of both the hydrogen absorbing conditions and the alloy conditions. Le. chemical composition, microstructure, and crystalline size, on the hydrogen decrepitation of Nd-Fe-B alloy were investigated in terms of H/M, and the basic mechanism of decrepitation processes related with the hydrogen absorbing conditions was revealed.View full abstractDownload PDF (1699K) -
Makoto Kinoshita, Katsumi Uemura, Tsutomu Yamamoto1997 Volume 44 Issue 1 Pages 96-101
Published: January 15, 1997
Released on J-STAGE: May 22, 2009
JOURNAL OPEN ACCESSκ-alumina films were deposited on WC-Co alloy by a CVD method with an under layer of TiC. Powder samples were also prepared by disolving steel sheets on which TiC/Al2O3 or TiC/Al2O3/TiN were deposited. These specimens were examined by X-ray diffraction to obtain more exact diffraction data for practical use.
Diffraction profiles of the films and the powders were analyzed with a hexagonal system. CVD-coated films showed strong orientation, namely c-axis being rectangular to the film plane. κ-Al2O3 has lattice constants of a0=9.632A and c0=8.929A as a hexagonal system. These values correspond to a0=4.816A, b0=8.342A and c0=8.929A of an orthorhombic system.View full abstractDownload PDF (376K) -
Osamu Terada, Hisashi Suzuki1997 Volume 44 Issue 1 Pages 102-105
Published: January 15, 1997
Released on J-STAGE: May 22, 2009
JOURNAL OPEN ACCESSMicrostructures and mechanical properties of the coarse-grained low-carbon WC-lomass%Co alloy having carbide grain size of 1.5-2.0 μm were mainly studied in relation to the amount of additional VC up to 5mass% in binder. It was found that the carbide grain size became uniform with increasing the amount of VC, because of suppression of the anomalous grain growth of WC. It was also found that transverse-rupture strength of the alloy was improved with increasing the amount of VC up to about 2-3mass%; however, it sharply decreased with additional amount of VC over about 3mass%. The phenomenon of this strength decrease, being never observed in micro-grained alloy, was attributed to the fact that (W, V)C phases crystallized so largly in the size in coarse-grained alloy, in contrast to micro-grained alloy, that it easily acted as a fracture source.View full abstractDownload PDF (3181K) -
Takehisa Ohno1997 Volume 44 Issue 1 Pages 106-110
Published: January 15, 1997
Released on J-STAGE: May 22, 2009
JOURNAL OPEN ACCESSCu-Zn composite nanoparticles were prepared by the condensation of Zn vapor onto flying Cu nanoparticles which were produced in advance by a gas-evaporation technique. The structural and morphological observation of these nanoparticles was carried out by means of a transmission electron microscope. It was found that most of the particles grown under the appropriate preparation conditions are composed of two phases of Cu-Zn alloy and Zn, where the latter surrounds the former. It is concluded that the particles grow through four steps; first, Cu nanoparticles grow, second, they melt and re-evaporate due to subsequent heating, and third, Zn vapor condenses onto them, and last, the condensed Zn atoms result in be alloyed with Cu atoms in the outer part of the particles.View full abstractDownload PDF (5702K) -
Masaru Yokoyama, Tetsuya Sato, Eiji Ohta, Toshihiko Sato1997 Volume 44 Issue 1 Pages 111-115
Published: January 15, 1997
Released on J-STAGE: May 22, 2009
JOURNAL OPEN ACCESSCation distribution, oxygen parameter and thermal parameter for bulk material and fine particles of CdFe2O4 were determined by X-ray powder diffraction based on the relation between In(Iobs/Ical) and sin2θ/λ2, where Iobs is the observed intensity, Ical is the calculated intensity, θ is the Bragg angle, and λ is the X-ray wavelength. The occupancy of Fe3+ ions at the A-sites is 0.06 and 0.13 for bulk material and fine particles with a size of-7 or-8nm, respectively. The cluster consisting of small number of Fe3+ ions at the B-sites are formed around a Fe3+ ion at the A-site through the A-B interactions. The oxygen parameters of the fine particles with size of-7 and -8 nm and the bulk material are 0.385, 0.389 and 0.391, respectively. The thermal parameters of the fine particles are approximately eighty times larger than that of the bulk material. The enhanced thermal parameter can be explained in terms of the softening on the surface.View full abstractDownload PDF (298K) -
1997 Volume 44 Issue 1 Pages 123
Published: 1997
Released on J-STAGE: May 22, 2009
JOURNAL OPEN ACCESSDownload PDF (17K)
- |<
- <
- 1
- >
- >|